Abstract
Lab-scale simulated biofilm reactors, including aerated reactors disturbed by short-term aeration interruption (AE-D) and non-aerated reactors disturbed by short-term aeration (AN-D), were established to study the stable-state (SS) formation and recovery after disturbance for nitrogen transformation in terms of dissolved oxygen (DO), removal efficiency (RE) of NH4+-N and NO3−-N and activity of key nitrogen-cycle functional genes amoA and nirS (RNA level abundance, per ball). SS formation and recovery of DO were completed in 0.56–7.75 h after transition between aeration (Ae) and aeration stop (As). In terms of pollutant REs, new temporary SS formation required 30.7–52.3 h after Ae and As interruptions, and seven-day Ae/As interruptions required 5.0% to 115.5% longer recovery times compared to one-day interruptions in AE-D and AN-D systems. According to amoA activity, 60.8 h were required in AE-D systems to establish new temporary SS after As interruptions, and RNA amoA copies (copy number/microliter) decreased 88.5%, while 287.2 h were required in AN-D systems, and RNA amoA copies (copy number/microliter) increased 36.4 times. For nirS activity, 75.2–85.8 h were required to establish new SSs after Ae and As interruptions. The results suggested that new temporary SS formation and recovery in terms of DO, pollutant REs and amoA and nirS gene activities could be modelled by logistic functions. It is concluded that temporary SS formation and recovery after Ae and As interruptions occurred at asynchronous rates in terms of DO, pollutant REs and amoA and nirS gene activities. Because of DO fluctuations, the quantitative relationship between gene activity and pollutant RE remains a challenge.
Highlights
Influent water stabilization to wastewater treatment systems (WWTSs) in terms of pollutant concentration and composition has been widely implemented as a strategy to stabilize the effluent water quality and realize sustainable operation [1,2]
For the AE-D reactors, 7.75, 5.25, and 4.36 h were required for the transformation from SS-AEDO to SS-ANDO after aeration was interrupted for 1, 7, and 14 days, respectively, while 0.76, 0.56, and 0.56 h, respectively, were required for the transition of SS-ANDO to the original SS-AEDO after aeration was restarted after aeration had been interrupted for 1, 7, and 14 days, respectively
For the AN-D reactors, aeration induced the transformation from SS-ANDO to SSAEDO over 0.70, 0.69, and 0.72 h after the 1, 7, and 14-day interruptions, respectively, while the aeration stop (As) conditions resulted in the recovery from the attained SS-AEDO to the original
Summary
Influent water stabilization to wastewater treatment systems (WWTSs) in terms of pollutant concentration and composition has been widely implemented as a strategy to stabilize the effluent water quality and realize sustainable operation [1,2]. Two kinds of strategies have been widely adopted to increase WWTS resilience, i.e., increasing the ability of a WWTS to handle shock loads and decreasing the load variation extent by building buffering facilities before pumping to the WWTS occurs. In large-scale integrated BR systems for wastewater treatment, stabilization, detention or aeration ponds are designed as the front end of sequential facilities to buffer any possible shock loads in terms of the quantity or composition [1,3,6]
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